The present invention relates to switching systems for telecommunications networks.
The Public Switched Telephone Network (PSTN) worldwide operates under a number of different standards. These standards indicate, among other things, methodology both for companding digital signals and for multiplexing these digital signals into carriers. Most of the world has digitized traffic that travels between Central Offices. There are two widely used standards for companding digital signals, known as A-law and xcexc-law standards. There are also two basic standards for multiplexing of voice signals, generally known as DS-1 and CEPT-1 for the lowest level multiplexed carriers. Generally xcexc-law and DS-1 are used in North America and A-law and CEPT-1 are used in Europe. The North American and European systems respectively may also be termed the North American hierarchy (Asynchronous Hierarchy) and the ITU Digital Hierarchy (Plesiochronous Digital Hierarchy).
Individual voice channels are digitized using either A-law or xcexc-law, into what is called DS-0 digital streams. These streams are then multiplexed into carriers using time division multiplexing (TDM) techniques. For North America, the DS-1 carrier is the lowest level multiplexed carrier, having up to 24 DS-0 channels per carrier, while in Europe the CEPT-1 carrier is the lowest level multiplexed carrier, having up to 30 DS-0 channels per carrier with two additional channels reserved for framing and optionally signaling or as an additional DS-0 channel.
Each of the above-mentioned multiplexed characters has their own control and synchronization functions, carried either in excess bits which are added into the stream or, as previously described, in a control channel set aside for this purpose. High order multiplexing exists, with a number of DS-1/CEPT-1 streams being multiplexed into ever higher carriers such as DS-3 for North America and CEPT-3 for Europe. In Japan, a different hierarchy is used. Fiber Optic Transmission systems use DS-3 or CEPT-3 as the basis for transmission, with added overhead for control and synchronization, and here too higher order multiplexing exists. In North America the standard for Fiber Optic Transmission is known as North American Synchronous Optical Network (SONET), whereas in Europe the Synchronous Digital Hierarchy (SDH) standard is used.
There often exists a need to cross connect between the two transmission standards, such as when a phone call is made from Europe to North Americaxe2x80x94a transatlantic call. In order to accomplish this, the signal is stripped down to the individual DS-0 level, converted from one companding method to the other, and remultiplexed using the appropriate techniques for the destination.
Digital Cross Connects are also well known in the art. In the United States, they are covered by a number of standards, including Bellcore TR-NWT-000233, which is incorporated herein in its entirety by reference. Digital Cross Connects are generally used to cross connect over a relatively long period of time a large number of multiplexed transmission streams, such as DS-1 or CEPT-1 streams. Some of the individual DS-0 channels which are part of the stream may be cross connected to other destinations, in which case the cross connect which is capable of this function is known as a 1/0 cross connect. In the event that higher order streams may be cross connected this would also be designated in the description of the cross connect, so that a cross connect that can individually connect DS-3, DS-2, DS-1, and their individual DS-0 signals would be described as a 3/2/1/0 cross connect. Bellcore Standard TR-NWT-000233, referenced above, describes the Generic Criteria of these cross connects.
In a standard layout of a prior art generic digital cross connect, as shown in FIG. 1, the signal first goes to a Transport Interface 10, and then it proceeds through the Cross Connect Matrix 12 to another Transport Interface 10 on the destination side. The transport interfaces at each side perform both physical layer functions and logical layer functions. Thus, any physical or logical transformations are carried out in the Transport Interface, prior to entering the Cross Connect matrix, or after leaving it. In the case of the typical transatlantic call mentioned above, the conversion method above would thus have to be done in the transport interface. It is to be noted that each input and output signal must be connected to a transport interface, and therefore the conversion function must be duplicated in each and every transport interface that is to perform the function. While other functions such as framing, logical error monitoring and facility data link in the DS-1 extended super frame (ESF) format may be handled in the transport interface, it would be more economical to not have to duplicate the conversion function, or other functions, in each and every transport interface.
A Digital Cross Connect for SONET is described in U.S. Pat. No. 5,365,518, and comprises an interface layer, a cross connect matrix, and an overhead server. The overhead server combines a multiplexer/demultiplexer and time slot interchanging circuitry with server controls and a switch module to handle both high-speed overhead and data through the matrix. Thus the server is capable of accomplishing cross connection of individual DS-0 streams. The system uses a SONET like signal throughout the matrix, and as a result the system can not be used to translate from North American to European standards in the server, since the matrix operates only under one standard. All conversions and other transport functions must be done in the transport interface prior to entering the matrix.
An electronic digital cross-connect system is known from U.S. Pat. No. 5,193,087. In this system the digital cross-connect is a space matrix, in which any input can be cross connected to any output with no significant time delay. The matrix uses a coded electronic signal to enable it to recreate at the output all aspects of the incoming signal, including any bipolar variations. However, again any conversion would have to he done in the transport interface. A Pulse Width Modulation (PWM) encoding technique is also described in U.S. Pat. No. 5,193,087.
A digital interface between different formats of digital signal is described in: Digital Interface Between the SLC96 Digital Loop Carrier System and a Local Digital Switch, TR-TSY-000008, Issue 2, August 1987.
T1 and E1 access signals cross-connect are governed by the following standards, respectively: Bellcore TR-170 and ITU-T G.796.
Thus there is a long felt need for a method of accomplishing functions of the transport interface in a more economical fashion.
The disclosures of all references mentioned above and throughout the present specification are hereby incorporated herein by reference.
There is thus provided in accordance with a preferred embodiment of the present invention a switching system for a telecommunications network, including a switching matrix, a transport interface for receiving signals from a plurality of I/O ports, the signals being arranged in channels of at least a first and a second format, a plurality of cross-connections for switching the signals between the I/O ports via the switching matrix, and a server operatively associated with the switching matrix and including format exchanging circuitry operable to receive a signal arranged in the first format and to rearrange the signal into the second format, thus producing a converted signal, and to transmit the converted signal to the switching matrix for eventual output.
Further in accordance with a preferred embodiment of the present invention the first format and the second format each include one of the following: at least part of the North American hierarchy (Asynchronous Hierarchy), at least part of the ITU Digital Hierarchy (Plesiochronous Digital Hierarchy), and at least part of the Japanese hierarchy, wherein the first format and the second format are not identical.
Still further in accordance with a preferred embodiment of the present invention the first format and the second format each have a tributary, and each tributary includes one of the following: an E-1 tributary, and a T-1 tributary. Additionally in accordance with a preferred embodiment of the present invention the cross-connections are operable to demultiplex channels in the first format and remultiplex channels in the second format.
Moreover in accordance with a preferred embodiment of the present invention the cross-connections are operable to perform, on the demultiplexed channels, at least one of the following: A-law to xcexc-law conversions, and xcexc-law to A-law conversions.
Further in accordance with a preferred embodiment of the present invention the plurality of cross-connections is included in the switching matrix, the switching matrix being operable to carry signals of the first format and the second format.
Still further in accordance with a preferred embodiment of the present invention the cross-connections further include a converting matrix operable to demultiplex channels, carry out at least one of A-law to xcexc-law conversions and xcexc-law to A-law conversions on the demultiplexed channels, and to remultiplex the channels.
Additionally in accordance with a preferred embodiment of the present invention the converting matrix is operable to carry out remultiplexing independently of demultiplexing.
Moreover in accordance with a preferred embodiment of the present invention channels received at the interface in one of the first format and the second format are passed to the switching matrix in the same one of the first format and the second format.
There is also provided in accordance with another preferred embodiment of the present invention a switching system for a telecommunications network, including a switching matrix, a transport interface for receiving signals from a plurality of I/O ports, the signals being arranged in multiplexed channels, a plurality of cross-connections for switching the signals between the I/O ports via the switching matrix, and a server operatively associated with the switching matrix and including circuitry operable to receive a signal arranged in the multiplexed format and to perform logical layer functions on the multiplexed channel, and to transmit the converted signal to the switching matrix for eventual output.
Further in accordance with a preferred embodiment of the present invention the logical layer function includes at least facility data link in the DS1 Extended Superframe Format.
There is also provided in accordance with another preferred embodiment of the present invention a method of converting signals arranged in multiplex channels of a first format to signals arranged in multiplex channels of a second format and routing the signals, including the steps of receiving the signals from a plurality of I/O ports, routing the signals over a matrix to a central converter, demultiplexing the channels of a first format into individual voice channels, converting the individual voice channels into channels of the second format, remultiplexing the channels of the second format, and routing the remultiplexed channels over a matrix to appropriate output ports.
Still further in accordance with a preferred embodiment of the present invention the first format and the second format each include one of the following: at least part of the North American hierarchy (Asynchronous Hierarchy), at least part of the ITU Digital Hierarchy (Plesiochronous Digital Hierarchy), and at least part of the Japanese hierarchy, wherein the first format and the second format are not identical.
Additionally in accordance with a preferred embodiment of the present invention the first format is E1 and the second format is T1.
Moreover in accordance with a preferred embodiment of the present invention the first format is T1 and the second format is E1.
Further in accordance with a preferred embodiment of the present invention the step of demultiplexing the channels of a first format into individual voice channels is followed by a step of A-law to xcexc-law conversion.
Still further in accordance with a preferred embodiment of the present invention the step of demultiplexing the channels of a first format into individual voice channels is followed by a step of xcexc-law to A-law conversion.
There is also provided in accordance with another preferred embodiment of the present invention a method of performing logical layer functions in switching system for a telecommunications network, including receiving signals from a plurality of I/O ports, the signals being arranged in multiplexed channels, providing a plurality of cross-connections for switching the signals between the I/O ports via the switching matrix, and providing a server operatively associated with the switching matrix to receive a signal arranged in the multiplexed format and to perform logical layer functions on the multiplexed channel, and to transmit the converted signal to the switching matrix for eventual output.
Further in accordance with a preferred embodiment of the present invention the logical layer function includes at least facility data link in the DS1 Extended Superframe Format.